The objective of this project is to gain some understanding of the role of two early functions of polyoma virus in transformation: the hr-t function and the ts-a function. Complementation between the two classes of transformation defective mutants representing the two functions govern different steps of transformation. This project deals with the analysis of the properties of transformed clones obtained by complementation, referred to as complementation clones. The particular interest lies in asking which viral gene(s) are required to be persistently expressed in complementation clones, and what is their relative topology in the host cell. The method involves the analysis of rescued virus, of the viral integration and of the proteins produced in the transformed cells.